Progress in the Development of Highly Efficient Photocatalytic Systems for Hydrogen Production from Water under Sunlight

Hydrogen production by photocatalytic water splitting under sunlight is one of the most promising approaches to addressing present day energy and environmental issues. For this reason, the research and development of systems for this purpose has recently accelerated on a worldwide basis. This review summarizes developments in the field of photocatalytic water splitting under visible light, especially systems using particulate photocatalysts. Focusing on visible-light-responsive photocatalyst materials, both one-step and two-step excitation systems are examined, as well as recently reported photocatalyst sheet systems in which particulate photocatalysts are fixed on a conductive plate. Some topics related to reactor designs incorporating UV-responsive model photocatalysts are also addressed. Finally, this review describes a demonstration of water splitting under actual sunlight using a 1 m x 1 m prototype reactor that exhibits a solar to hydrogen conversion efficiency of approximately 0.4 %.